Read-after-write magnetic heads for digital signals are usually installed in computer peripheral devices, and are provided with plural pairs of read/write gaps for a plurality of channels. When a magnetic tape passes above such a magnetic head, a digital signal is written on the tape in a writing gap. Immediately thereafter, the tape passes above a reading gap, and said signal is read out to check the correctness of the signal.
Frequencies in a high-frequency range of about 1 to 3 MHz are used for writing or readout of digital signals by the magnetic head to achieve a high-density recording. Therefore, core materials used for the magnetic head are required to have high magnetic permeabilities and also high saturation magnetic flux densities. Heretofore, permalloy which has been worked into thin sheets of about 25 to 50 .mu.m thickness has been used as a core material. A certain number of thin sheets of permalloy are stacked on top of each other and bonded together by a molded resin such as epoxy resin.
The magnetic permeability of these laminas of permeability decreases to the range from about 600 to 800 at 1 MHz when internal stress is produced by the molded resin or mechanical tightening. In case where the core material having a poor frequency characteristic in this way is used, signal waveforms result in phase shift at high frequencies, impairing the symmetry of signal waveforms. This reduces the reliability of the computer peripheral devices.